The present invention relates generally to devices for injecting two or more medications simultaneously and, more particularly, to a removable manifold assembly that is attachable to the outlet end of the injection device for mixing the two medications and discharging the mixed medications through a single needle.
It is medically desirable in the treatment of certain conditions of the human body to administer two or more types of medications simultaneously. The treatment of diabetes is one such example. Under certain conditions, it is desirable to simultaneously deliver two types of insulin, fast-acting insulin and an intermediate-acting insulin, such as isophane insulin, which takes effect more slowly but for a longer period of time. Also, a longer-acting type of insulin called ultralente is available. In order to most accurately simulate the natural glucose curve of the body, the insulin user would need to inject different ratios or combinations of these insulins several times daily.
In order to achieve such injection capability, there have been developed injection devices in which separate cartridges of a desired medication are housed. It is desirable that both medications be delivered to a patient through a single needle instead of two or more needles. Therefore, such injection devices must have a manifold assembly that enables the medications to be mixed together prior to injection.
An example of such an injection device is disclosed in U.S. Pat. No. 5,253,785. This patent discloses a manifold assembly consisting of a rear piece (spike adaptor 116) and a front piece (manifold 118), both made of hard plastic, and rubber check valve body disposed therebetween. The check valve body includes a pair of cup-shaped members, each having an internal conical surface positioned to engage an external conical surface formed by the outside of a respective hollow projection in the front piece to form a check valve. Normally, the check valves are closed thereby preventing fluid flow from a common pathway that fluidly connects to the interior of the needle cannula. Upon pressurization of the interior of one of the cartridges, the corresponding check valve is opened by deformation of the check valve body. To permit this deformation, there is an annular gap surrounding the cup-shaped members and a further gap in the space between that portion of the check valve body adjacent to the cup-shaped members and the rear piece.
Another type of manifold assembly is disclosed in U.S. Pat. No. 5,271,527. This manifold assembly is removable from the cartridge housing of the dispenser in order to permit the removal and replacement of the spent cartridges of medication. A pair of manifold assembly release buttons are mounted to the housing. To remove the manifold from the housing, the release buttons are forced toward the manifold assembly until pegs extending from the cartridge housing become disengaged from holes formed in tabs on the manifold housing, thereby permitting the user to pull the manifold assembly away from the housing.
Another type of manifold assembly is disclosed in PCT International Application Number PCT/US93/11044 (International Publication Number WO 94/11039). This application discloses a dual chamber pharmaceutical dispenser having a manifold including a check valve associated with each chamber for permitting fluid flow from the chamber into the manifold flow path. These check valves are each formed by a valve insert and a cylindrical elastic band mounted over the valve insert to permit the flow of liquid pharmaceutical in one direction only. A ball check valve is provided to prevent the flow of fluid from the pharmaceutical chamber to the needle assembly. Upon depressing the manifold shield to initiate an injection, the ball of the check valve is moved away from the valve seat to permit fluid flow through the needle cannula.
Although the disclosed manifold check valves are designed to prevent the flow of fluid back into the pharmaceutical reservoirs, these valves may experience wear and deformation over time, resulting in leakage. It is desired to provide a manifold assembly that improves upon known check valve structures in order to more positively prevent a reverse flow of fluid back into the pharmaceutical reservoirs. In addition, it is desired to provide a removable manifold assembly for a reusable injection dispenser that minimizes the likelihood of contamination of the cartridges upon placement of the manifold onto the new cartridges.